Using the I/0 port of the microcontroller to do a key input experiment

The I/0 port of a typical microcontroller is a quasi-bidirectional port, which can be used as both an output port and an input port. In specific operations, we write data out of the I/0 port to use it as an output port; if we directly call the current state of the I/0 port in the program, assign values ​​to our defined variables, or use it for operations such as logical judgment and branch control, we use it as an input port.

The figure below shows the circuit that uses the P2.0 port to read the button control.

As can be seen from the figure below, in this circuit, port P2.0 is an input application. When the button is not pressed, +5V is connected to P2.0 through the pull-up resistor R1, and the voltage of port P2.0 is +5V, which is logic "1". If the button is pressed, P2.0 is connected to the power ground through the button, and the voltage of port P2.0 is 0V, which is logic "0".

To sum up, when no key is pressed, the state of P2.0 is "1"; when a key is pressed, the state of P2.0 is "0".

If there is no resistor R1, when the button is pressed, the +5V power supply will be short-circuited to the ground through the button, which may seriously damage the power supply. This is absolutely not allowed.

Assume that the microcontroller is connected to the circuits in the above and below figures at the same time, use P2.0 as the input port, read the key: use P3.4 to control the buzzer. Write a program that makes the buzzer sound when the key is pressed and stops when the key is not pressed. The program is as follows:

#include

sbitBuzzer=P3^4;sbitKey=P2^0;//[Note 1]

//Main program voiDMAin(void){for(;;){if(Key==0){//【Note 2】

Buzzer=0; //The button is pressed and the buzzer sounds}

else{Buzzer=1;//The button is not pressed, the buzzer stops beeping}

}

【Note 1】：The bit variable Key is defined as the P2.0 port of the microcontroller. The subsequent operations on the variable Key are the operations on the P2.0 port.

【Note 2】: Conditional statement, directly use the state of Key (that is, the state of P2.0 port) to control the operation of the program. If the key is pressed, the state of P2.0 is 0, Key=0 is true, the program executes Buzzer=0, and the buzzer sounds; if the key is not pressed, the state of P2.0 is 1, Key=0 is false, the program executes Buzzer=1, and the buzzer stops sounding.